1. Field of the Invention
The present invention relates to image recording and reproduction apparatuses, and more particularly, to an image recording and reproduction apparatus that can operate in a first display mode for displaying a first display screen in which an image is constituted by a first number of horizontal scanning lines and a second display mode for displaying a second display screen in which an image is constituted by a second greater number of horizontal scanning lines.
2. Description of the Background Art
A digital still camera is an electronic image recording and reproduction apparatus that can record and store image data value obtained from a solid state image sensing device such as a CCD onto a single recording medium such as a semiconductor memory and view a reproduced image through a display device such as a liquid crystal display device (LCD). By connecting the digital still camera to a monitor device, the reproduced image can also be viewed through the monitor device.
FIG. 4 is a circuit block diagram showing a structure of a conventional digital still camera. Referring to FIG. 4, a conventional still camera includes a CCD 1, a CDS/AGC circuit 2, an A/D converter 3, a signal processing circuit 4, an image compression circuit 5 and an image memory 6. The still camera also includes an image expansion circuit 7, a display memory 8, a display circuit 9, an D/A converter 10, an LCD 11, a character data set circuit 21, a switch 22, an NTSC character font memory 23, and a
character font memory 24. D/A converter 10 can be connected to an external monitor device by means of a connector and the like.
The overall operation of this still camera will be described briefly hereinafter. Incident light through a lens not shown is converted into an analog image signal by CCD 1. The signal output from CCD 1 has its level adjusted by CDS/AGC circuit 2, and then converted into a digital signal by A/D converter 3. Here, the data amount matches the number of pixels of CCD 1. One color data corresponding to a color filter of CCD 1 is present per one pixel.
The signal output from A/D converter 3 is subjected to various processes such as pixel interpolation and matrix processing by signal processing circuit 4 to be converted into image data of Y, U and V. These image data are provided for each of all the pixels. Y corresponds to a luminance signal, and U and V correspond to two types of color difference signals.
The image data is compressed by image compression circuit 5 and recorded into image memory 6. When the JPEG system, for example, is employed as the compression system, the screen is divided into a plurality of blocks of 8.times.8 pixels as shown in FIG. 5. Data compression is carried out for each component of Y, U and V on a block-by-block basis.
In order to reproduce an image, the compressed data is read out from image memory 6. The readout data is expanded into the former Y, U and V data by image expansion circuit 7 to be written into display memory 8. Here, characters of numerics and signs are also written into display memory 8. More specifically, switch 22 is altered according to whether the monitor device complies with the NTSC method or the PAL method, whereby the appropriate NTSC character font memory 23 or PAL character font memory 24 is connected to character data set circuit 21. Character data set circuit 21 reads out the character data from the connected memory 23 or 24 to provide the read out data into display memory 8.
The image data and character data in display memory 8 are read out by display circuit 9 to be converted into analog signals by D/A converter 10. The converted analog signals are provided to LCD 11 and an external monitor device.
Switching is provided between character font memory 23 and 24 depending upon whether the monitor device complies with the NTSC system or the PAL system because the vertical to horizontal ratio of the display screen differs depending upon the system of the monitor device. More specifically, as shown in FIG. 6, an image is formed of 480 lines in the vertical direction and 640 pixels (dots) in the horizontal direction in the NTSC system. In the PAL system, an image is formed of 570 lines in the vertical direction and 640 pixels in the horizontal direction. Therefore, an arrangement is provided so that the position of the characters in the display screen does not differ according to the system employed by the monitor device by arranging the character image formed of 46 lines.times.36 pixels in 9 rows and 15 columns at the middle of display screen for a monitor device of the NTSC system and a character image formed of 54 lines.times.36 pixels in 9 rows and 15 columns at the middle of the display screen for a monitor device of the PAL system. It is to be noted that the horizontal scanning lines are skipped in FIG. 6 although there are 525 lines and 625 lines in the vertical direction in the NTSC system and the PAL system, respectively.
The operation of character display will be described in detail hereinafter. Data which are designs of character fonts for NTSC and PAL are respectively prepared in advance for character font memories 23 and 24. In the present specification, the operation of providing a character display on a monitor device according to the NTSC method will be described.
In order to display a character on the basis of two colors such as white for the character itself and black for the background, font data as shown in FIG. 7 is prepared. This example of FIG. 7 shows the display of the alphabet letter "I" in 36 pixels.times.46 lines. By providing a display of black for the pixel of 0 and white for the pixel of 1 in FIG. 7, a white character "I" is formed within a black rectangle. This image is sequentially read out starting from the leftmost upper pixel to the bottom rightmost pixel into predetermined addresses of display memory 8. More specifically, 1 (01) and 2 (10) are written into the predetermined addresses of display memory 8 when character data=0 and character data=1, respectively, as shown in FIG. 8.
In order to write both image data of Y, U and V data and character data into display memory 8, 8 bits are allotted for Y data and 6 bits are allotted for each of U and V data. The character data of 1 or 2 is written into the least significant 2 bits of each U and V data. The image and character data for one screen are recorded as described above into display memory 8.
As shown in FIG. 9, display circuit 9 includes character level set registers 31-33, a character level select circuit 34, and switches 35 and 36. Character level set registers 31-33 provides levels 1-3 corresponding to the color to be displayed by respective pixels. The three switch terminals 35a-35c of switch 35 receive the outputs from character level set registers 31-33, respectively. Switch 36 has one switch terminal 36a receiving the output of display memory 8 and the other switch terminal 36b connected to a common terminal 35d of switch 35. A common terminal 36c of switch 36 is connected to D/A converter 10. Switches 35 and 36 are controlled by character level select circuit 34.
The character data corresponding to the leasts significant 2 bits of each U and V data in display memory 8 takes four types of values from 0-3 including the above-described 1, 2. When character data is 0, connection across terminals 36a and 36c of switch 36 is established so that the background image data in display memory 8 is applied to D/A converter 10. When character data is 1-3, the connection across terminals 36b and 36c of switch 36 is established, so that the outputs of character level set registers 31-33 are applied to D/A converter 10. By presetting the relationship between the output level and the color of the pixel such as a black level for output level 1 of register 31 and a white level for output level 2 of register 32, a display of a character such as that shown in FIG. 7 can be provided.
Although the above description is provided for character display on a NTSC system monitor device, similar character display can be achieved on a PAL monitor device by writing character data into display memory 8 according to the data of PAL character font memory 24 shown in FIG. 4.
The conventional digital still camera had the disadvantage that a relatively large memory capacity is required since two types of character fonts for both the NTSC and PAL systems have to be prepared.